71. Arithmetic Logic Unit

How do you plan to solve it?

module alu4(input [3:0]a,b,input [2:0]op,output reg [3:0]y,output reg cf);
    reg carry;
    always @(*) begin
        carry = 1'b0;
        case(op) 
            3'b000: begin
                {carry,y} = a+b;
                cf = carry;
            end
            3'b001: begin
                {carry,y} = {1'b0,a}+{1'b0,(~b)}+1;
                cf = ~carry;
            end
            3'b010: begin
                y = a&b;
                cf=1'b0;
            end
            3'b011: begin
                y = a|b;
                cf = 1'b0;
            end
            3'b100: begin
                y = a^b;
                cf = 1'b0;
            end
            default: begin
                y = 4'b0000;
                cf = 1'b0;
            end
        endcase
    end
endmodule